The present invention relates to circuits for controlling the output level of a load and, more particularly, to a novel load output level control circuit having a single input for receiving a control signal for providing both on/off and output level information to a controllable load.
The ability to control the output level of a load facilitates many economic advantages in this day and age of energy conservation. With the advent of variable load-output level controls, such as are found in the variable-output gas-discharge lamp/ballast system of copending U.S. Patent application Ser. No. 177,942, filed Aug. 14, 1980, to the assignee of the present invention and incorporated herein by reference, control of fluorescent lamp light output is now practical. Such a lamp-ballast load requires both an on/off input and an output-level-setting input for proper control. Variable impedances may be utilized for on/off and level-setting control; however, greatest acceptance of such variable output level control systems require that the control signal(s) be generated equally as well at a location adjacent to, or a location remote from, the location at which the load control circuit is positioned. Thus, greatest economy is provided if a single signal-carrying circuit is utilized between the input of a control circuit (itself providing both the on/off and level-setting signals to the ballast/lamp load) and some remote location at which the control input signal is generated. Further, greatest cost advantage occurs if the on/off and output-level-setting signals are derivable from a single signal, whereby multiplexing techniques and apparatus are not required.